while we have lift unit off also have pulled off radiator and had it cleaned and checked due to 2 inches of gunk in bottom of housing. radiator cap is shot, now needing to replace can any one tell me which type to use, Pressure or nonpressure.
this is a 1964 cup.

If you want the old style non-pressurized cap then that is Part# 351030R91
which is replaced Part #400584R1. If I remember correctly when I got mine the replacement is actually a pressure cap. If you want the original, you will have to find someone with NOS.

I think my dealer said the gasket was still available for the old style cap is you want to rehabilitate yours.